Plaque: House sparrow pavement plaque
A smaller stone in the lower right corner seems to be part of the overall design and has some markings on it but we could make nothing of them.
Site: House sparrow pavement plaque (1 memorial)
NW1, Cardington Street, St James Gardens
Nicholas Booth spotted this plaque and noticed its similarity to our two puzzle pavement plaques: the palmette in Euston Road and the Egyptian eye in Hampstead Road. We are sure it is one of the same series - it's in the same style (icon + arrow) and refers to a nearby feature (assuming sparrows like gardens), though in this case not architectural. But frustratingly we are no closer to knowing why these plaques were placed, nor if there are any more. All three are in Camden so it seems likely that Camden Council were involved. We will write to a friendly Councillor and ask.
2015: There's a fourth, the Euston Arch.